<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="js/vue.js"></script>
</head>
<body>
    <div id="app">
        {{ test }}
    </div>
    <script>
        var app = new Vue({
            el: "#app",
            data: {
                test:"helow world"
            },
            watch:{
                test(val){
                    console.log("状态改变了",val)
                }
            }
        });
    </script>
    <!-- 当状态改变的时候触发watch里面的test方法 -->
</body>
</html>